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发点科学知识、少儿不宜

Y chromosome
The Y chromosome is the one of the two sex-determining chromosomes in humans. The human Y chromosome is composed of about 60 million base pairs.

Most humans have one pair of sex chromosomes in each cell. Males have one Y chromosome and one X chromosome, while females have two X chromosomes. The Y chromosome also contains other genes needed for normal sperm production.
There are exceptions, however, some men have two Xs and a Y (ie "XXY", aka Klinefelter's syndrome), or one X and two Ys (ie XYY syndrome). There are other exceptions in which SRY (ie Sex-determining Region Y) is damaged (leading to an XY female), or copied to the X (leading to an XX male).
In humans, the Y chromosome spans about 58 million base pairs (the building blocks of DNA) and represents approximately 2% of the total DNA in a human cell. The human Y chromosome contains 86 genes, which code for only 23 distinct proteins. Traits that are inherited via the Y chromosome are called holandric traits.
The human Y chromosome is unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions at the telomeres (which comprise about 5% of the chromosome's length). These regions are relics of ancient homology between the X and Y chromosomes. The bulk of the Y chromosome which does not recombine is called the "NRY" or non-recombining region of the Y chromosome. It is the SNPs in this region which are used for tracing direct paternal ancestral lines.

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1楼2010-08-20 12:28回复

Haplogroup
In the study of molecular evolution, a haplogroup is a group of similar haplotypes that share a common ancestor with a single nucleotide polymorphism (SNP) mutation. Because a haplogroup consists of similar haplotypes, this is what makes it possible to predict a haplogroup from haplotypes. An SNP test confirms a haplogroup. Haplogroups are assigned letters of the alphabet, and refinements consist of additional number and letter combinations, for example R1b1. Y-chromosome and mitochondrial DNA haplogroups have different haplogroup designations. Haplogroups pertain to deep ancestral origins dating back thousands of years.
In human genetics, the haplogroups most commonly studied are Y-chromosome (Y-DNA) haplogroups and mitochondrial DNA (mtDNA) haplogroups, both of which can be used to define genetic populations. Y-DNA is passed solely along the patrilineal line, from father to son, while mtDNA is passed down the matrilineal line, from mother to offspring of both sexes. Neither recombines, and thus Y-DNA and mtDNA change only by chance mutation at each generation with no intermixture between parents' genetic material.

2楼2010-08-20 12:29

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Human Y-chromosome DNA haplogroups
In human genetics, a Human Y-chromosome DNA haplogroup is a haplogroup defined by differences in the non-recombining portions of DNA from the Y chromosome (called Y-DNA).
The Y chromosome consortium has established a system of defining Y-DNA haplogroups by letters A through to T, with further subdivisions using numbers and lower case letters.
Y-chromosomal Adam is the name given by researchers to a theoretical male who is the most recent common patrilineal (male-lineage) ancestor of all living humans. Estimations of the date of this common ancestor have varied significantly in different studies.

3楼2010-08-20 12:29

7楼2010-08-20 12:30

Distribution of Haplogroup F
Besides the major clades G, H, IJ, and K, other patrilines derived from Haplogroup F-M89 can still be detected at a very low frequency among many populations of the southern fringe of Eurasia and Oceania, from Portugal in the west to Korea and the Malay Archipelago in the east. India, Korea, and the Ailao Mountains of Yunnan Province in southwestern China appear to be the only regions where such lineages, which are grouped for convenience as Haplogroup F*, comprise a significant portion of the Y-chromosome diversity of the modern populations. Haplogroup F* Y-chromosomes have been found to be particularly common among the Kucong or Yellow Lahu, a group of hunter-gatherers who live in the Ailao Mountains of Yunnan. Korean F* probably reflects a rare brother clade of haplogroups G, H, IJ, and K that may have experienced a geographically limited expansion during historical times, as such Haplogroup F* Y-chromosomes have not been found among the neighboring Japanese.

8楼2010-08-20 12:31

9楼2010-08-20 12:31

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